Field of the Invention
The present invention relates generally to recovery of petroleum crude oil from subterranean hydrocarbon reservoirs and, more particularly, to systems and methods for in-situ recovery of petroleum crude oil or bitumen from deposits of sand and shale.
Description of the Related Art
Steam Assisted Gravity Drainage (SAGD) is one of the techniques for recovering tar-sand based high viscosity hydrocarbons or heavy oil, or commonly known as crude oil or bitumen, from subsurface geologic formations or reservoirs. The high viscosity of the crude oil or bitumen, which can exceed 106 centipoise, prevents it from flowing at natural reservoir temperatures; therefore, the bitumen deposits cannot be economically exploited by traditional oil well recovery technologies.
As shown in the example in FIG. 1, in conventional SAGD techniques, at least two parallel horizontal wellbores 11A and 11B can be drilled in a crude oil bearing formation 10, one approximately 5 meters above the other. The SAGD processes generally includes heating the high viscosity crude oil through the upper wellbore 11A by continuously injecting steam 12 into it so that the steam, possibly mixed with solvents, forms a steam chamber in the formation.
The heat from the continuously injected steam reduces the viscosity of the high crude oil and thus improves its mobility. The lower wellbore 11B collects the heated low viscosity crude oil that flows out of the formation, along with any water from the condensation of injected steam. The fluid mixture 14 entering the lower wellbore 11B is then pumped to the surface 16 for refining and oil production.
However, the SAGD techniques exhibit various problems that affect productivity and efficiency. In addition to the cost of drilling well pairs, steam generation and the associated emissions are major concerns in assessing the economic potential of such recovery operations.
One major problem is the requirement for large amounts of energy to produce the steam and hence deliver sufficient heat to stimulate the heavy oil bearing reservoir. Such required large amounts of energy is usually obtained by burning natural gas which is often available in the tar-sand fields, which also generates unwanted gas emissions, particularly carbon dioxide emissions causing environmental pollution. Furthermore, difficulties in maintaining or controlling the temperature of the crude oil during the extraction can also pose difficulties.
From the foregoing, therefore, there is a need for a novel system and a method, which overcomes the many disadvantages of the conventional heavy crude oil recovery technologies, for efficiently mobilizing and recovering a significant amount of crude oil from subsurface heavy crude oil reservoirs.